Other
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998dps....30.0602i&link_type=abstract
American Astronomical Society, DPS meeting #30, #06.02; Bulletin of the American Astronomical Society, Vol. 30, p.1022
Other
Scientific paper
Mars Orbiter Laser Altimeter (MOLA) is an instrument on board of Mars Global Surveyor spacecraft. The laser operates at 1.064 micron wavelength, emitting 8-nsec-long pulses. MOLA measures topography, reflectivity and returned pulse width. Here we will discuss reflectivity and interpret it in terms of atmospheric opacity. Reflectivity is a ratio of the returned energy to the emitted energy. It can be interpreted as a product of albedo (A) of the Martian surface and two-way atmospheric transmission ( R = A * e({) -2 tau }), where tau is atmospheric opacity. Attenuation of the MOLA signal in the atmosphere is only due to extinction of photons from the laser beam. There are practically no photons scattered into the laser beam. This allows us a very straightforward calculation of opacity, given albedo of the surface. We will present opacity calculations based on IRTM bolometric channel albedo map and red-filter camera images and discuss problems associated with opacity calculations based on these datasets. We were able to obtain values for atmospheric opacity at the MOLA wavelength (1.064 micron) during hiatus orbits (L_s = 180-220) and Science Phasing Orbits (SPO) (L_s = 300 - 367). Preliminary assessment of the results for the equatorial regions indicates clear atmosphere during start of SPO (L_s = 300-316), then opacity peaks at L_s = 330 and slowly decreases till the end of SPO observations. At the same time two other instruments (TES and MOC) on MGS were performing measurements of opacity at their corresponding wavelengths (9 micron and 0.7 micron). Atmospheric opacity is a function of the wavelength due to the scattering properties of the aerosols. We will present our approach for comparison opacity measurements at MOLA, MOC and TES wavelengths. This comparison will allow us to determine particles size distribution properties, which is an important parameter for atmospheric heating.
Ivanov Boris A.
Muhleman Duane O.
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